QUOTE(jod @ Jul 19 2006, 10:15 AM)

Jo-jingles or Kodaly kindergarten come to mind immediately. Singing nursery rhymes at home, and making sure music is going on around them. Allowing children to respond through movement, or even by bashing a wooden spoon against a saucepan.
If you're only going in for one session, then there's not enough time to start a theme, or for the children to really learn some new songs.
If you plan to go in regularly, then a brilliant book is Babies Make Music, Kids Make Music Too - loads of ideas for developing music with young children. Also Bobby Shaftoe Clap Your Hands, and An Early Start in Music.
For a one-off session, try musical statues - play something jazzy/folky and get them to dance, then stop when you stop (at random places!)
If you have a tambourine or a similar jingly instrument, try sitting in a circle and passing it round really quietly. I have a special song for this, but maybe you could make up your own? Then see how loudly you can pass it round before finishing with quietly.
Show them three or four small different-sounding percussion instruments, then put them inside a box or bag, play one, and let them see if they can say which one it was. Let the children do the playing, too.
There are lots of other things to do - pre-school classes are my favourite - but hopefully this will give you some ideas. Enjoy!